1. Field of the Invention
The invention relates to a road surface division mark recognition apparatus, and a lane departure prevention apparatus. More particularly, the invention relates to a road surface division mark recognition apparatus and a lane departure prevention apparatus that maintain high serviceability ratio even at high temperature.
2. Description of the Related Art
In recent years, a lane departure prevention apparatus that includes a white line recognition portion that recognizes a white line on a road on the basis of a picked-up image acquired by a vehicle-mounted camera, and a steering control portion that controls the steering so that the vehicle does not depart from the traveling lane, on the basis of the positional relationship between the vehicle and the white line recognized by the white line recognition portion has been being put to practical use.
As an image pickup element of the vehicle-mounted camera, a CCD (charge coupled device) is used in many cases. The vehicle-mounted camera is often provided near a cabin-side site on an upper portion of the windshield, and the vicinity of the windshield is likely to have high temperature due to the influence of sunshine. The imaging performance of the CCDs is susceptible to be affected by thermal electrons that occur at high temperature. If a CCD is affected by thermal electrons, noise occurs in picked-up images. If the amount of noise occurring in a picked-up image increases, there arises a possibility of the white line recognition portion failing to accurately recognize a white line on a road. If the white line recognition portion fails to accurately recognize a white line, it may become impossible for the lane departure prevention apparatus to certainly prevent the vehicle from departing from the traveling lane.
A technology described in Japanese Patent Application Publication No. 2001-88609 (JP-A-2001-88609) prevents a vehicle-mounted camera from operating at high temperature. This technology measures the temperature of the vehicle-mounted camera, and stops the action of the vehicle-mounted camera by stopping the supply of electric power to the vehicle-mounted camera if the measured temperature of the camera is higher than or equal to a threshold value. This prevents the vehicle-mounted camera from operating at such a high temperature that much noise occurs in a picked-up image.
However, when the vehicle-mounted camera has stopped, the white line recognition portion cannot recognize a white line, and the lane departure prevention apparatus cannot prevent lane departure of the vehicle. Therefore, at high temperature, the serviceability ratio of the lane departure prevention apparatus declines. Hence, a white line recognition apparatus and a lane departure prevention apparatus whose decline in serviceability ratio is minimized even at high temperature have been desired.